Temperature-dependent exciton dynamics in J-aggregates-when disorder plays a role

Area of Science:

• Materials Science
• Photochemistry
• Supramolecular Chemistry

Background:

• J-aggregates are ordered molecular assemblies with unique optical properties.
• Classical J-aggregates, like pseudoisocyanine (PIC), are primarily held by van der Waals forces.
• Perylene bisimide (PBI) dyes offer tunable properties for advanced materials.

Purpose of the Study:

• Investigate the spectral properties of core-tetrasubstituted PBI J-aggregates.
• Compare the temperature-dependent behavior of PBI J-aggregates with classical J-aggregates (THIATS).
• Understand the role of disorder and hydrogen bonding in PBI J-aggregate properties.

Main Methods:

• Absorption and fluorescence spectroscopy.
• Temperature-dependent measurements (300 K to 5 K).
• Comparative analysis with existing data for THIATS J-aggregates.

Main Results:

• PBI J-aggregates exhibit significantly broader absorption bands than THIATS J-aggregates, indicating substantial disorder.
• Both PBI and THIATS J-aggregates show similar qualitative temperature dependence of the Stokes shift.
• PBI J-aggregates display unexpectedly low thermal activation energy for exciton migration.

Conclusions:

• Hydrogen bonding contributes to the structure of PBI J-aggregates alongside van der Waals forces.
• Disorder significantly influences the spectral properties and exciton dynamics in PBI J-aggregates.
• The findings provide a deeper understanding of exciton behavior in disordered supramolecular systems.